This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to a Japanese Patent Application 2002-045196, filed on Feb. 21, 2002, the entire content of which is incorporated herein by reference.
This invention generally relates to a seat vertical position adjusting device for lifting up and down a front-end portion of a seat cushion so as to adjust a height of the front-end portion thereof.
A conventional seat vertical position adjusting device has been disclosed as a Japanese Patent Laid-Open published as No. 2000-190762. A driving mechanism including a brake mechanism and a pinion gear is equipped to a frame portion supporting a front-end portion of the seat cushion. The frame portion is pivotably supported by a bracket member mounted on a floor. A sector gear possessing a large pitch circle is assembled to the bracket member and is engaged with the pinion gear. The pinion gear can be rotated via the brake mechanism in response to operation of an operation handle so that the frame portion is pivotably rotated, thereby the front-end portion of the seat cushion can be effectively adjusted to be lifted up or down. Further, the front-end portion of the seat cushion can be maintained at an intended position by use of the brake mechanism.
However, the operating force for operating the seat vertical position adjusting device disclosed above is increased when an occupant is seated on the seat cushion. In this case, a speed reducing ratio of the pinion gear and the sector gear can be increased for reducing the operating force of the seat vertical position adjusting device. However, the pinion gear can be downsized with a certain limitation so as not to weaken the engagement force of the pinion gear with the sector gear. On the other hand, a size-up of the sector gear results in a size-up of the seat vertical position adjusting device and an increase of the weight thereof. Accordingly, the speed reducing ratio can be increased only to a certain level so that a relatively large operating force is required to operate the seat vertical position adjusting device.
The present invention therefore seeks to provide an improved seat vertical position adjusting device which can be operated with a small operating force even when the front-end portion of the seat cushion is applied with an occupant""s load.
A seat vertical position adjusting device of the present invention includes a seat cushion applied with a load when an occupant is seated thereon, a base plate portion supporting the seat cushion, a cushion frame housed in the seat cushion and supported by the base plate portion so as to be movable in a vertical direction, and a driving mechanism equipped to one of the cushion frame and the base plate portion for driving the cushion frame to be movable in the vertical direction relative to the base plate portion.
The driving mechanism includes a shaft having a first axial portion and a second axial portion which is positioned on the first axial portion, eccentrically rotated relative to the first axial portion, and connected to a driving member, a stationary gear member fixed to the one of the cushion frame and the base plate portion, mounted on one side of the first axial portion, and having a first internal gear, a driving arm connected to the other one of the cushion frame and the base plate portion, mounted on the other side of the first axial portion, having a second internal gear of which number of gear teeth is different from the number of gear teeth of the first internal gear, and disposing the second axial portion between the driving arm and the stationary gear member, and a pinion gear mounted on the second axial portion and engaged with the first and second internal gears.